Mechanical Susceptibility of a Rotaxane.

We have investigated the mechanical dissociation of an ammonium/crown ether rotaxane using experimental (sonication) and computational (CoGEF) methods and found that it breaks faster than its noninterlocked or uncoupled interlocked (i.e., pulled from both sides of the axle) counterparts. This was confirmed by the analysis of the fragments, which are the results of a selective unstoppering reaction. Interestingly, the initial dissociation also triggered the elimination of the axle segment separating the stopper from the ammonium binding station. CoGEF calculations have shown that the constriction of the axle by the macrocycle during the elongation of the rotaxane provokes the accumulation of tensile and torsional stress that ultimately leads to the rupture of a covalent bond in the constricted section of the axle. Overall, these results suggest that the rotaxane architecture acts as a lever that accelerates the dissociation of interlocked covalent bonds. This phenomenon could impact the mechanical properties of slide-ring materials at high strain.